Catalytic cracking and dehydrocyclizing of alkanes using alkaline earth oxides promoted with manganese oxide and/or rhenium oxide

ABSTRACT

Alkanes are catalytically converted employing a catalyst comprising at least one alkaline earth oxide together with a promoting amount of manganese oxide and/or rhenium oxide. When the catalyst is treated with an oxygen-containing gas, such as air, prior to contacting the alkanes conversion by cracking is favored. When the catalyst is treated with hydrogen prior to contacting the alkanes dehydrocyclization is favored. A composition of matter is disclosed suitable for use as a catalyst for converting alkanes.

RELATED APPLICATION

This application is a continuation in part of my copending applicationSer. No. 460,935 filed Apr. 15, 1974, now abandoned.

BACKGROUND OF THE INVENTION

The invention relates to a composition of matter suitable as a catalyst,and a method for converting alkanes, including a method for crackingalkanes using the catalyst and a method for dehydrocyclizing alkanesusing the catalyst.

Catalytic cracking and dehydrocyclizing of various hydrocarbonsconstitute a very important part of most refining operations. Althoughmany catalysts are known for such processes, catalytic cracking anddehydrocyclizing are areas of continuing research in an effort to findnew and better processes and catalysts.

An object of the invention is to crack alkanes.

Another object of the invention is to dehydrocyclize alkanes.

Another object of the invention is to crack or dehydrocyclize alkanesusing a catalyst.

Still another object of the invention is to provide a catalyst suitablefor cracking alkanes or dehydrocyclizing alkanes.

Other objects, aspects, and advantages of the invention will be apparentto those skilled in the art upon studying the specification and theappended claims.

SUMMARY

According to the invention, a composition of matter is providedcomprising at least one alkaline earth oxide together with a promotingamount of a compound selected from the group consisting of manganeseoxide and rhenium oxide.

Further, according to the invention, alkanes are converted employing acatalyst of the above composition.

Further, according to the invention, alkanes are catalytically crackedemploying a catalyst comprising at least one alkaline earth oxidetogether with a promoting amount of a compound selected from the groupconsisting of manganese oxide and rhenium oxide wherein said catalyst istreated with a dry oxygen containing gas at a high temperature prior tocontacting the alkanes.

Still further, according to the invention, alkanes are catalyticallydehydrocyclized employing a catalyst comprising at least one alkalineearth oxide together with a promoting amount of a compound selected fromthe group consisting of manganese oxide and rhenium oxide wherein saidcatalyst is treated with hydrogen at a high temperature prior tocontacting the alkanes.

DETAILED DESCRIPTION OF THE INVENTION

Alkaline earth oxides, namely the oxides of magnesium, calcium,strontium, and barium, are useful in this invention. Oxides ofmagnesium, calcium and strontium are especially useful. A single oxide,such as calcium oxide, can be promoted with manganese oxide and/orrhenium oxide; or mixtures of alkaline earth oxides, such as magnesiumoxide and calcium oxide or magnesium oxide and strontium oxide, can bepromoted with manganese oxide and/or rhenium oxide.

The proportions of the alkaline earth oxides where more than onealkaline earth oxide is employed is not believed to be critical. For thedehydrocyclization embodiment magnesium oxide and calcium oxide inweight ratios of from 100/1 to 5/1 produced good results and arepreferred. For the embodiment wherein alkanes are cracked the bestresults were obtained using a mixture of magnesium oxide and eithercalcium oxide or strontium oxide in approximately 20/1 to 8/1 weightratio with a promoter. Where one alkaline oxide was used with a promoterto crack alkanes, the best results were obtained using calcium oxide.

Oxides of either manganese and/or rhenium are useful as promoters forthe above described catalysts. While it is recognized that bothmanganese and rhenium are capable of existing in a range of oxidationstates, the precise nature of the promoting species of this inventionhas not been determined. One skilled in the art, after examination ofthe preparation procedure for the cracking catalyst, will readilyrecognize that the promoting species of this invention are undoubtedlyamong the higher oxidation states available for manganese or rhenium. Inthe case of the dehydrocyclization catalyst, the hydrogen treatment mayreduce the manganese and rhenium. For sake of simplicity and ease ofcalculation the promoting species for both the cracking anddehydrocyclization catalyst are hereinafter referred to as Mn₂ O₇ andRe₂ O₇, although it is recognized that the actual promoted catalyst isthe reaction product resulting from the admixture, under suitablecatalyst-forming and catalyst-activating conditions, of suitablealkaline earth metal compounds and manganese and/or rhenium compounds.

It is not presently believed that the amount of promoter employed iscritical. From 0.1 to 30 parts by weight of the promoting compound per100 parts by weight alkaline earth oxide or mixture thereof is generallyadequate to produce the desired results. It is currently preferred touse in the range of from about 1 to 15 parts by weight promoter per 100parts by weight alkaline earth oxides since good results were obtainedemploying this range.

The catalyst system including promoter and alkaline earth oxide(s) canbe prepared by any convenient means such as dry blending, slurryblending, solution blending, etc. In the preparation of the inventivecatalysts, oxides of manganese and/or rhenium and alkaline earth metals,or compounds of these elements which are convertible to the oxide oncalcination, are combined in any suitable catalyst-forming method. Thecatalysts can be in any suitable form, such as pellets, pills,agglomerates, and powders. Before use, the catalyst is heated under astream of the appropriate treating agent or gas as described herein at atemperature ranging from about 750° to about 1200° F (about 400°-650° C)for a period of time ranging from about 0.1 to about 20 hours.

Where the cracking of alkanes is to be favored according to oneembodiment of the invention, the catalyst above described is treatedwith a dry oxygen-containing gas. Where the dehydrocyclization ofalkanes is to be favored according to another embodiment of theinvention, the catalyst above described is treated with hydrogen. Thehydrogen treatment can either replace the oxygen-containing gastreatment or the hydrogen treatment can follow the oxygen-containing gastreatment. Whichever treating gas is used, it is frequently consideredbeneficial to flush the treated catalyst with an inert gas such asnitrogen prior to contact with the feed.

It is pointed out that whether the catalyst is treated with a dryoxygen-containing gas or hydrogen, reactions carried out employing suchcatalysts involve both cracking and dehydrocyclization reactions. Thehydrogen treatment of the catalyst enhances the dehydrocyclizationactivity of the catalyst, but the hydrogen-treated catalyst alsoproduces a substantial quantity of cracked products.

It is currently convenient to prepare the catalyst according to thefollowing procedure. A weighed amount of an oxide, such as magnesiumoxide, is slurried with a water solution containing the appropriateamount of a nitrate of another alkaline earth metal, such as calciumnitrate or strontium nitrate. After evaporation of the water from theslurry, the dried solid is reslurried with a water solution of anappropriate nitrate as for example, manganese (II) nitrate or rhenium(II) nitrate. After evaporation of the water from the slurry, the driedsolid is ground, sieved and treated with a dry oxygen containing gas orhydrogen at a temperature ranging from about 950° to about 1050° F (510°to about 566° C) for a period of time ranging from about 1 to about 4hours. Good results were obtained by treating the catalyst at atemperature of 1000° F (538° C) for 4 hours. The above proceduredescribes the preparation of a catalyst containing a mixture of alkalineearth oxides. When a single alkaline earth oxide is desired, theslurrying with the alkaline earth nitrate solution is omitted. Rheniumis applied to the catalyst as described above except that an aqueoussolution of ammonium perrhenate is used.

Feedstocks capable of being cracked by the catalyst system of thisinvention include any of the normal cracking feedstocks containinglinear or branched saturated hydrocarbons referred to generally asalkanes. These can be crude oil fractions or other refinery streams. Thedesired mixture of products will generally determine the selection offeedstock. For example, one feedstock may be more suitable to producegasoline than another.

Feedstocks capable of undergoing dehydrocyclization in the presence ofthe catalyst system of this invention include any of the above-describedfeeds containing substantial quantities of linear or branched saturatedalkanes containing 6 or more carbon atoms per molecule. Preferred alkanecomponents of the feedstock contain carbon chains of 6 or more carbonatoms in a chain either unsubstituted or substituted with one or morealkyl side chains. Of course, the products obtained employing either thecracking or dehydrocyclization embodiments of the invention aredependent on the feedstock to a large extent.

Any type of reactor normally used in catalytic cracking ordehydrocyclizing operations can be used with the catalyst system of thisinvention. For example, fixed bed, fluidized bed, trickle bed, etc.,reactors can be employed, though fluidized bed reactors are usually usedin commercial processes.

Reaction conditions suitable for catalytic cracking ordehydrocyclization vary widely. The reaction conditions depend to someextent upon the feedstock and the desired products. Temperatures arenormally in the range of from about 450° to about 600° C (842° to about1112° F), although temperatures from about 525° to about 575° C (977° toabout 1067° F) have produced good results. Space velocity of feedstockis dependent to a large extent upon the specific conditions such asfeedstock, temperature, diluent, desired products, ets., but a spacevelocity sufficient to provide a contact time of 0.1-50 seconds isgenerally desirable. Pressures are ordinarily near atmospheric butpressures in the range of from about 0-200 psig can be used.

It may be desirable in some cases to employ a diluent. Inert diluentssuch as nitrogen may be used, or it may be advantageous to use hydrogengas to control dehydrogenation, coke formation, and productdistribution.

It is often advantageous to periodically regenerate the catalyst bed byany suitable means, such as treatment with dry air at elevatedtemperatures. Such regeneration generally removes deposits of coke whichcan be formed in varying amounts during the cracking ordehydrocyclization reaction.

EXAMPLES

In the following examples a pulse-type reactor was employed. The reactorwas 1 cm O.D. by 30.5 cm long which included a catalyst bedapproximately 3 cm long. The analyzer was a gas-liquid chromatograph(glc). A feed injector introduced 3 to 5 microliter pulses of feedstockinto the reactor at desired time intervals and temperatures. Thecatalysts were prepared employing the slurry blending as hereindescribed.

EXAMPLE I

In this example n-heptane was cracked to produce C₁ to C₃ productsemploying various catalysts of the invention. The amount of catalystused was varied and so was the temperature of the process. Several runsat various temperatures were made employing a reactor without a catalystand employing a reactor containing only quartz to establish a basis forcomparison of the results employing the inventive catalysts. The reactorwas initially flushed with dry air at 1000° F (538° C) for 4 hours andthen with helium at 3-5 psig for 15 minutes prior to introducing thefeed into the reactor. Air was allowed to flow through the reactor atthe desired reaction temperature for 30 minutes between feed pulses.Residence time of feed in the reactor was approximately 1 second and thepressure was 3 psig. The reaction temperature, catalyst, catalystamount, catalyst weight ratio, and results are provided in Table I. Inthis example and the following examples conversion represents weightpercent of feed converted into C₁ to C₃ products including minor amountsof hydrogen gas. Also selectively represents weight percent of feedconverted into volatile products.

    TABLE I      Cracking of n-Heptane Catalyst   CaO/Mn.sub.2 O.sub.7  CaO/Mn.sub.2     O.sub.7  MgO/Mn.sub.2 O.sub.7  MgO/CaO/Mn.sub.2 O.sub.7       MgO/SrO/Mn.sub.2 O.sub.7  MgO/CaO/Mn.sub.2 O.sub.7  MgO/CaO/Mn.sub.2     O.sub.7  CaO/Re.sub.2 O.sub.7 Wt. Ratio Temp.  95/5 9/1 95/5 90/9/1     90/9/1 88/9/3 85/10/5 95/5 Amount ° C None Quartz 1 ml 2 ml 1 ml     2 ml 1 ml 1 ml 2 ml 1 ml 2 ml 1 ml 1 ml 2 ml       Conversion 450       37        Selectivity  23.sup.(a) 22.sup.(a)     8.sup.(a) Conversion 500  2  2  7 11 12 17 70  8   6     4 Selectivity     77 82 75 73 81 78 51.sup.(a) 81  80    84 Conversion 525  5  6   22   15      11  15 12 Selectivity  76 76   82   82  83  85 80 Conversion 550 11 15     21 29 32 30 85 25 24 20 45 25 20 20 Selectivity  78 78 78 78 84 82 36 83     87 82 90 86 82 89 Conversion 575 26 18   50   39  34 46 38 34 37     Selectivity  80 82   87   84  85 86 87 86 85     .sup.(a) Major amount of hydrogen formed. Not included in selectivity.

The above runs establish the operability of the invention. Most of theinventive runs showed a substantial improvement in both conversion andselectivity over the runs employing a reactor without a catalyst orcontaining only quartz, particularly at the higher crackingtemperatures.

EXAMPLE II

Another series of runs was made identical to the conditions used inExample I with the exception that the feed was 3-methylhexane. Resultsare shown in Table II.

                                      TABLE II                                    __________________________________________________________________________    Cracking of 3-Methylhexane                                                    Catalyst       None                                                                             Quartz                                                                            CaO/Mn.sub.2 O.sub.7                                                                 CaO/Mn.sub.2 O.sub.7                                                                 CaO/Re.sub.2 O.sub.7                                                                 MgO/CaO/Mn.sub.2 O.sub.7                                                                MgO/SrO/Mn.sub.2                                                              O.sub.7                  Wt. Ratio             95/5   9/1    95/5   90/9/1    90/9/1                   Amount  Temp., ° C                                                                       1 ml                                                                              1 ml                                                                             2 ml                                                                              2 ml   2 ml   1 ml      1 ml 2                   __________________________________________________________________________                                                              ml                  Conversion %                                                                          500                                 6         6                       Selectivity %                              90        86                       Conversion %                                                                          525                                 9                                 Selectivity %                              87                                 Conversion %                                                                          550    13 14  20     23     19     20        18   37                  Selectivity %  70 72  80     83     93     86        85   90                  Conversion %                                                                          575                                33        34                       Selectivity %                              87        86                       __________________________________________________________________________

The above results were consistent with the results of Example I.

EXAMPLE III

Additional runs were made employing either 2,3,3-trimethylbutane or2,4-dimethylpentane as the feed. The reaction conditions were the sameas in the previous examples. The results are given in Table III.

                                      TABLE III                                   __________________________________________________________________________    Cracking of 2,2,3-Trimethylbutane and 2,4-Dimethylpentane                                   2,2,3-Trimethylbutane    2,4-Dimethylpentane                                             MgO/CaO/                                                                              MgO/SrO/  MgO/CaO/                                                                              MgO/SrO/                   Catalyst          CaO/Mn.sub.2 O.sub.7                                                                 Mn.sub.2 O.sub.7                                                                      Mn.sub.2 O.sub.7                                                                        Mn.sub.2 O.sub.7                                                                      Mn.sub.2 O.sub.7           Wt. Ratio         9/1    90/9/1  90/9/1    90/9/1  90/9/1                     Amount        None                                                                              1 ml   1 ml    1 ml  None                                                                              1 ml    1 ml                       Run No. Temp., ° C                                                                   Run 1                                                                             Run 2  Run 3                                                                             Run 4                                                                             Run 5 Run 6                                                                             Run 7                                                                             Run 8                                                                             Run 9                      __________________________________________________________________________    Conversion, %                                                                         500    4  11     13  11   7     3   9   4   4                         Selectivity, %                                                                              61  65     69  83  72    54  79  68  66                         Conversion, %                                                                         525   12 24                                                                             27     12  13   8    21   8   9                             Selectivity, %                                                                              63  65     65  66  61    56  62  68  65                         Conversion, %                                                                         550   27  36     48  26  26    16  32  18  17                         Selectivity, %                                                                              58  66     64  65  59    59  64  69  65                         Conversion, %                                                                         575   48  54     72  49  45    27  44  34  33                         Selectivity, %                                                                              59  70     68  67  61    63  67  71  69                         __________________________________________________________________________

The above results were consistent with the results of Examples I and II.Although it was not determined why a discrepancy existed between theresults in runs 3 and 4 and in runs 7 and 8, it is noted thatselectivity was better in the runs in which the inventive catalyst wasused as compared to the runs in which no catalyst was used.

EXAMPLE IV

This example illustrates the dehydrocyclization embodiment of thisinvention.

A catalyst corresponding to CaO/Mn₂ O₇ /MgO in the weight ratio 3/7/90,respectively, was prepared as described earlier by impregnating MgO withaqueous solutions of calcium nitrate followed by manganous nitrate.After drying, grinding and sieving the catalyst was treated withhydrogen gas or dry air at 1000° F (538° C) for 1 hour followed bynitrogen gas for 5 minutes. Passing n-heptane over the thus-preparedcatalysts at 1022° F (550° C) and atmospheric pressure at a rate of 1 gmfeed per 1 ml catalyst per hour gave the results tabulated in Table IV.

                  Table IV                                                        ______________________________________                                        Dehydrocyclization of n-Heptane                                                                 Catalyst Treatment                                                            Hydrogen  Air                                               ______________________________________                                        n-Heptane conversion, %.sup.a                                                                     21.8        14.5                                          Aromatics selectivity, %.sup.b                                                                    20          2                                             Cracking selectivity, %.sup.c                                                                     80          98                                            ______________________________________                                         .sup.a Conversion to products.                                                .sup.b Predominantly toluene.                                                 .sup.c Percent of total volatile organic products containing less than 7      carbon atoms.                                                            

These data show that substantial amounts of aromatic products,especially toluene, are formed from n-heptane by use of the inventiveprocess. These results also show that hydrogen-treatment results inhigher conversion to products and higher selectivity to aromatics thandoes treatment with an oxygen containing gas.

EXAMPLE V

This example illustrates the dehydrocyclization embodiment of theinvention utilizing catalysts of varying composition.

Catalysts corresponding to CaO/Mn₂ O₇ /MgO in various weight ratios wereprepared and treated with hydrogen as described in Example IV. n-Heptanewas utilized as feed through the reactor at conditions of temperature,pressure and feed rate as described in Example IV. Data are recorded inTable V.

                  Table V                                                         ______________________________________                                        Varying Catalyst Composition                                                                n-Heptane  Aromatic  Cracking                                   CaO/Mn.sub.2 O.sub.7 /MgO                                                                   Conv., %   Select., %                                                                              Select., %                                 ______________________________________                                        1/9/90        24         31        69                                         3/7/90        30         9(95).sup.a                                                                             .sup.a                                     2.5/2.5/95    18         15        85                                         5/5/90        20         14        86                                         7.5/7.5/85    19         26        74                                         7/3/90        21         15        85                                         9/1/90         9         .sup.b    .sup.b                                     ______________________________________                                         .sup.a Anomalous and inconsistent results not explained.                      .sup.b Information not available.                                        

The above data show that a wide range of compositions containing CaO,Mn₂ O₇ and MgO are useful in the dehydrocyclization embodiment of theinvention.

EXAMPLE VI

This example illustrates the dehydrocyclization embodiment of theinvention utilizing the catalyst and treatment thereof and reactionconditions as described in Example IV. Compounds with 6 or 7 carbonatoms and containing C₄ to C₇ carbon chains were utilized as feedstock.Data are tabulated in Table VI.

                  Table VI                                                        ______________________________________                                        Variable Feedstock                                                                                    Aromatic   Cracking                                                 Conv.,    Select.,   Select.,                                   Feedstock     %         %          %                                          ______________________________________                                        n-Heptane     25.0      9.4        90.6                                       2-Methylhexane                                                                              23.1      11.0       89.0                                       3-Methylhexane                                                                              26.6      9.1        90.9                                       2,2-Dimethylpentane                                                                         24.9      1.0        99.0                                       2,3-Dimethylpentane                                                                         29.3      1.9        98.1                                       2,4-Dimethylpentane                                                                         20.5      2.1        97.9                                       2,2,3-Trimethyl-                                                              butane        26.2      0.8        99.2                                       ______________________________________                                    

These data illustrate that various feeds are useful in obtainingaromatic products, but those containing carbon chains of 6 or morecarbon atoms provide higher selectivity to aromatics.

What is claimed is:
 1. A method for catalytically converting alkanescomprising contacting the alkanes under converting conditions with acatalyst by forming a reaction mixture consisting essentially of saidalkanes and a catalyst consisting essentially of components selectedfrom the group consisting of:(A) two alkaline earth oxides and apromoting amount of a promoter selected from the group consisting ofmanganese oxide and a mixture of manganese oxide and rhenium oxide, (B)at least one alkaline earth oxide and a promoting amount of rheniumoxide, and (C) an alkaline earth oxide selected from the groupconsisting of strontium and barium and a promoting amount of a promoterselected from the group consisting of manganese oxide and a mixture ofmanganese oxide and rhenium oxide.
 2. The method of claim 1 wherein thepromoting amount is in the range of from about 0.1 to about 30 parts byweight per 100 parts by weight alkaline earth oxide.
 3. The method ofclaim 1 wherein the promoting amount is in the range of from about 1 toabout 15 parts by weight per 100 parts by weight alkaline earth oxide.4. The method of claim 1 wherein the alkaline earth oxide in (A) and (B)is selected from the group consisting of magnesium, calcium, andstrontium.
 5. The method of claim 1 wherein the alkanes arecatalytically cracked employing the catalyst which is treated with dryair at a temperature in the range of from about 750° to about 1200° F(approximately 400° to about 650° C) for a period of time ranging fromabout 0.1 hour to about 20 hours prior to contacting said alkanes. 6.The method of claim 5 wherein the cracking temperature is in the rangeof from about 450° to about 600° C (842° to about 1112° F); wherein thecracking pressure is in the range of from about 0 to about 200 psig; andwherein the feed-to-catalyst contact time is in the range of from about0.1 to about 50 seconds.
 7. The method of claim 5 wherein the alkalineearth oxide in (A) and (B) is a mixture of magnesium oxide and calciumor strontium oxide, the weight ratio of magnesium oxide to calcium orstrontium oxide is in the range of from about 20:1 to about 8:1, and thecatalyst is treated at a temperature ranging from about 950° to about1050° F (510° to about 566° C) for a period of time ranging from about 1to about 4 hours.
 8. The method of claim 1 wherein the alkanes arecatalytically dehydrocyclized employing the catalyst which is treatedwith hydrogen at a temperature in the range of from about 750° to about1200° F (approximately 400° to about 650° C) for a period of timeranging from about 0.1 hour to about 20 hours prior to contacting saidalkanes, and wherein said alkanes are linear or branched substituted orunsubstituted alkanes having 6 or more carbon atoms per molecule.
 9. Themethod of claim 8 wherein the alkanes contain carbon chains of at least6 carbon atoms, either unsubstituted or substituted with one or morealkyl side chains.
 10. The method of claim 8 wherein thedehydrocyclization temperature is in the range of from about 450° toabout 600° C (842° to about 1112° F); wherein the dehydrocyclizationpressure is in the range of from about 0 to about 200 psig; and whereinthe feed to catalyst contact time is in the range of from about 0.1 toabout 50 seconds.
 11. The method of claim 8 wherein the alkaline earthoxide in (A) and (B) is a mixture of magnesium oxide and calcium orstrontium oxide, the weight ratio of the magnesium oxide to calcium orstrontium oxide is in the range of from about 100:1 to about 5:1, andthe catalyst is treated at a temperature ranging from about 950° toabout 1050° F (510° to about 566° C) for a period of time ranging fromabout 1 to about 4 hours.